ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Uneven, Uneven, ConchoidalArthur Thomas, Gemstones (2009)
SiO 2(+Al 2O 3)Walter Schumann , Gemstones of the world (2001)
Na 4AlBeSi 4O 12ClMichael OâDonoghue , Gems, Sixth Edition (2006) More from other references